Cream together butter and sugar until light and fluffy.
Add eggs and beat until incorporated.
Add milk, sour cream, almond extract, baking powder, and salt. Mix until fully combined.
Mix in flour until just incorporated. Set aside.
Prepare the Plum Layer & Assemble
Cut plums into thin wedges.
In a bowl, mix together butter and brown sugar.
Grease a 10-inch round cast iron skillet*. Pour sugar mixture into the the pan and spread evenly over the bottom.
Arrange plum wedges in a single layer over the sugar.
Gently spread cake batter over the plum layer.
Bake for 30-35 minutes or until toothpick inserted in the center comes out clean or with a few moist crumbs.
Allow the cake to cool for 5-10 minutes before inverting onto a plate. To invert: Run a butter knife around the edge of the cake to ensure it is released from the sides of the skillet. Place a large plate over skillet, hold them firmly together and quickly flip allowing the cake to release onto the plate.
Allow the cake to cool before slicing and serving.
Notes
*You can use a cake pan or pie pan in place of a cast iron skillet, but you may need to increase the baking time. Dark pans, such as cast iron, tend to cook things faster.
Keyword easy fruit dessert, fall dessert, plum dessert, summer dessert, upside down cake